框架源码 – springboot启动过程

启动原理run

springboot启动代码

@SpringBootApplication
public class AppApplication { 
  public static void main( String[] args ){
      SpringApplication.run(AppApplication.class, args);
  }
}

进入SpringApplication类的run（）方法

//SpringApplication类的run方法
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
   return run(new Class[]{primarySource}, args);
}
//调用重写的方法
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
    //由此可知启动类做了两个事情，一个是创建springapplication对象，再一个是执行run方法
    return (new SpringApplication(primarySources)).run(args);
}

由以上代码可知启动类做了两个事情：一个是创建springapplication对象，再一个是执行run方法

创建SpringApplication对象

new SpringApplication(primarySources)

public SpringApplication(Class<?>... primarySources) {
this((ResourceLoader)null, primarySources);
}

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
    this.sources = new LinkedHashSet();
    this.bannerMode = Mode.CONSOLE;
    this.logStartupInfo = true;
    this.addCommandLineProperties = true;
    this.addConversionService = true;
    this.headless = true;
    this.registerShutdownHook = true;
    this.additionalProfiles = new HashSet();
    this.isCustomEnvironment = false;
    this.lazyInitialization = false;
    this.resourceLoader = resourceLoader;
    Assert.notNull(primarySources, "PrimarySources must not be null");
    this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
    this.webApplicationType = WebApplicationType.deduceFromClasspath();
    this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
    this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
    this.mainApplicationClass = this.deduceMainApplicationClass();
}

WebApplicationType.deduceFromClasspath();

• 加载应用类型

• NONE

• 该应用程序不应作为Web应用程序运行，也不应启动嵌入式Web服务器

• SERVLET

• 默认springboot启动上下文类型就是servlet

• REACTIVE

• 该应用程序应作为反应式Web应用程序运行，并应启动嵌入式反应式Web服务器

this.getSpringFactoriesInstances(ApplicationContextInitializer.class)

• 初始化spring factory

• ＭETA-INF/spring.factories

this.getSpringFactoriesInstances(ApplicationListener.class)

• 初始化监听器

• ＭETA-INF/spring.factories

this.deduceMainApplicationClass()

• 通过遍历 StackTrace 来查找到启动类

run()方法

run（）方法源码

public ConfigurableApplicationContext run(String... args) { 
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
    this.configureHeadlessProperty();
    SpringApplicationRunListeners listeners = this.getRunListeners(args);
    listeners.starting();

    Collection exceptionReporters;
    try {
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
        ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
        this.configureIgnoreBeanInfo(environment);
        Banner printedBanner = this.printBanner(environment);
        context = this.createApplicationContext();
        exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
        this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
        this.refreshContext(context);
        this.afterRefresh(context, applicationArguments);
        stopWatch.stop();
        if (this.logStartupInfo) {
            (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
        }

        listeners.started(context);
        this.callRunners(context, applicationArguments);
    } catch (Throwable var10) {
        this.handleRunFailure(context, var10, exceptionReporters, listeners);
        throw new IllegalStateException(var10);
    }

    try {
        listeners.running(context);
        return context;
    } catch (Throwable var9) {
        this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
        throw new IllegalStateException(var9);
    }
}

run()方法主要内容详解

• StopWatch stopWatch = new StopWatch();
  stopWatch.start();
• 开启计时器
• this.configureHeadlessProperty();

• 设置加载外设环境

• SpringApplicationRunListeners listeners = this.getRunListeners(args);
  listeners.starting();

• 获取监听器

• ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);

• 初始化环境
• java -jar test.jar --server.port=8888

• 执行jar 参数server.port=8888
• –server.port=8888

• 初始化外部参数

• this.prepareEnvironment(listeners, applicationArguments)

• 加载准备环境

• 把外部环境加到系统运行环境中

• this.configureIgnoreBeanInfo(environment)

• 配置忽略BeanInfo

• Banner printedBanner = this.printBanner(environment);

• 创建输出内容
• 类型

• OFF
• CONSOLE
• LOG

• context = this.createApplicationContext();

• SERVLET

• org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext

• REACTIVE

• org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext

• default

• org.springframework.context.annotation.AnnotationConfigApplicationContext

• this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);

• ＭETA-INF/spring.factories

• this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
• this.refreshContext(context);

• this.prepareRefresh();

• 初始化一些配置属性，验证配置文件

• ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();

• 获取beanFactory

• this.prepareBeanFactory(beanFactory);

• 将context中的一些属性设置到beanFactory中

• this.postProcessBeanFactory(beanFactory);

• 注册Scope相关的类

• this.invokeBeanFactoryPostProcessors(beanFactory);

• 解析配置文件、生成所有的beanDefinitions

• this.registerBeanPostProcessors(beanFactory);

• 分类、排序、注册（注入）所有的BeanPostProcessors，用于处理 bean 的初始化流程

• this.initMessageSource();

• 多语言转化

• this.initApplicationEventMulticaster();

• 注册 applicationEventMulticaster

• this.onRefresh();

• 主要创建并初始化容器

• this.registerListeners();

• 事件注册监听者

• this.finishBeanFactoryInitialization(beanFactory);

• 主要是初始化非懒加载单例

• this.finishRefresh();

• 主要是开启Web容器

• this.afterRefresh(context, applicationArguments);
• (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);

• 开启日志

• this.callRunners(context, applicationArguments);

• 执行启动后加载

• listeners.running(context);

介绍getSpringFactoriesInstances()方法

这个方法全文出现三次

• 1.首先尝试从内存缓存中获取，如获取到就立即返回，没有则继续下面内容；
• 2.从类加载路径（的jar文件）中获取全部的spring.factories文件路径；
• 3.循环遍历读取这些文件中的键值对(K->List[V])；
• 4.将读取内容放入内存缓存，下次再调用这个方法时会优先从缓存中获取；
• 5.返回读取到的全部键值对集合（Map[K,List[V]]结构）。